Hot wire relay type devices and methods of maintaining or producing such devices

ABSTRACT

A hot wire relay type device, formed from an alloy composition exhibiting a characteristic of mechanical shape memory as a result of martensitic-type transformation, is operatively maintained or produced for use as a heat reactive controller in a way so that the supported termination portions do not react to heat or, at the very least, heat above transition simultaneously with the portion of the device intermediate such termination portions whereby the wire achieves a thermal balance throughout its entire body.

United States Patent Tyler [151 3,684,994 1 1 Aug. 15,1972

[54] HOT WIRE RELAY TYPE DEVICES AND METHODS OF MAINTAINING OR PRODUCING SUCH DEVICES [72] Inventor: Hugh Jean Tyler, Santa Ana, Calif.

[73] Assignee: Robertshaw Controls Company,

Richmond, Va.

[22] Filed: July 2, 1969 [21] Appl. No.: 838,501

[52] US. Cl ..337/140, 337/395 [51] Int. Cl.,..H01h 37/32, HOlh 37/50, HOlh 61/00 [58] Field of Search ..29/183, 183.5, 191.6, 193,

[56] References Cited UNITED STATES PATENTS 3,516,082 6/1970 Cooper ..337/393 X 3,402,238 9/1968 Buehler et a1. ..337/393 3,280,550 10/1966 Cassidy ..60/23 3,254,100 5/1966 Flanagan ..337/140 X 3,243,797 3/1966 Smith ..340/270 3,174,851 3/1965 Buehler et a1 ..337/393 UX 3,142,149 7/1964 Hays ..60/23 2,983,974 5/1961 Tebb et a1 ..24/33 2,306,187 12/ 1 942 Ronan ..29/95 1,556,285 10/ 1 925 Chrabkow ..267/74 1,517,130 11/1924 Wike ..267/74 3,450,372 6/1969 Lange et a1 ..75/170 Primary Examiner-Bemard A. Gilheany Assistant Examiner Dewitt M. Morgan Attorney-Auzville Jackson, Jr., Robert L. Marben and Anthony A. O'Brien 5? ABSTRACT 10 Claims, 7 Drawing Figures HOT WIRE RELAY TYPE DEVICES AND METHODS OF MAINTAINING OR PRODUCING SUCH DEVICES BACKGROUND OF THE INVENTION 1. Field of the Invention This invention generally appertains to improvements in temperature responsive devices and, more particularly, relates to new and novel improvements in hot wire relay type devices for use as thermal reactive controllers for operating or actuating drive, switch or motor devices in response to a supplied heat within a predetermined temperature range.

2. Description of Prior Art The provision of hot wires and their use for controlling various devices, such as an electrical switch, drive mechanism, motor mechanism or the like, is well known in the prior art wherein bimetallic filaments, thermally expansible wires and the like are employed for operating control or work mechanisms with the essence of the construction being resident in the fact that the wire changes dimension simply on the basis of having a thermal coefficient of expansion.

Such known devices do not possess good stability and are not extremely and critically reliable in quick and positive temperature reactive sensitivity and, furthermore, such known structured hot wire relay type devices do not have dimensional stability in the repeated performance of their control or work functions in response to internal or external heat applications.

SUMMARY OF THE INVENTION The present invention relies upon an alloy composition exhibiting the unusual characteristic of shape memory as the result of martensitic-type transformation. An example of such alloy composition is a nickeltitanium alloy which has many advantages over bimetallic composites, one being that it produces more useful work per unit weight of metal. Such nickeltitanium alloy preferably has 50 to 70 percent nickel content by weight and from about 50 to 30 per cent titanium by weight with the alloy having the structure of a TiNi phase in combination with a TiNi phase dispersed in a TiNi matrix within a temperature range of about 500 to about 75 C.

While the foregoing specifically defined nickeltitanium alloy has been found to be of inestimable value in the present invention because it exhibits the unusual characteristic of possessing a mechanical memory, the present invention finds its value in utilizing other materials with a mechanical shape memory even though they may not be of such particularly delineated nickel-titanium composition.

An important aspect of the materials employed resides in the unusual characteristic of shape or mechanical memory. By this is meant that a straight wire of a material can be bent or contorted below its martensitic transition temperature and it will retain its formed shape, but when the deformed wire is heated above its transition temperature with nothing constraining its free movement, such wire will immediately spring back to its original straight shape.

An engineering description of such material in its transition is to say that it has a curve of increasing modulus with increasing temperature and another curve of decreasing modulus with decreasing temperature. This description applies to either Modulus of Elasticity or to Modulus in Torsion as shown, for example, by FIGS. 1 and 2, respectively, of US Pat. No. 3,403,238 to Buehler et a].

In general, such material is used in a complete cycle, that is, the control or work mechanism applies a load to the memory material that will cause the material to deform when it is cold and, to complete the cycle, heat is applied from a medium being controlled or supplied from a power source to cause the material to perform work. The supplied heat causes the material to try to return to the annealed shape it had before it was deformed. The mechanisms for applying load and heat to the material should be such that they allow the material to go through complete cycles with an excess of work available for control or work functions, with no loss of dimensional stability.

To make a practical application using the hot strength of such wire, the wire must be heated uniformly to prevent overstressing the sections below transition temperature. If the wire is clamped by conventional means at the ends, the ends remain cooler and, therefore, soft, but the center portion of the wire heats above transition and becomes hard with a higher modulus of elasticity. The maximum allowable stress that can be used is, therefore, the allowable stress of the soft, cool ends of the wire unless some way can be found to harden the ends independent of temperature or allow the ends to heat at the same rate as the center of the wire.

Accordingly, an object of the present invention is to provide methods of maintaining or producing a uniformly hard wire when the wire is heated above its transition point as byan electrical current.

Another object of the present invention, inasmuch as the wire is prone to encounter temperatures along the length thereof differing from those at the supported ends, is to apply various termination methods to the ends whereby a more reliable and stronger end anchoring is produced with the ends being hardened so that they have no transition or have a transition differing from the transition temperature of the active center portion intermediate such end portion.

Another object of the present invention is to provide means for thermally distributing heat in a hot wire relay to achieve thermal balance throughout the wire body.

This invention has a further object in that a hot wire is formed in such a manner as to highly stress sections of the hot wire, which are readily heated to above transition temperature but to reduce the stress in sections which are slow to heat and thereby stay soft and below the transition temperature.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a side elevational view of a wire clamped by conventional means at its ends, with such clamping means being shown in vertical section and the supported or anchored ends of the wire being hard at all times in relation to the uniformly heated center section wherein a modulus change is obtained.

FIG. 2 is a side elevational view of another form of terminating arrangement for the wire wherein the clamped ends of the wire are hardened by a process such as chromium infusion.

FIG. 3 is a side elevational view of still another form of wire wherein the supporting ends are formed from a hard material which has no transition and which supporting ends are welded to the ends of the transition wire in advance of the conventional supporting clamps, which are shown in vertical section.

FIG. 4 is a side elevational view of still another embodiment of-the present invention wherein although thermal balance is not achieved along the length of the body, the stress is reduced by virtue of smaller diameter loops at the ends to a low enough stress level to allow the soft wire to be easily supported by clamps which are shown in vertical section.

FIG. 5 is a side elevational view of still another form of the present invention wherein thermal balancing of the wire body is achieved by adding a mass to the center of the wire body so as to achieve slow heating in the portion of the wire body intermediate the ends thereof until the clamped ends are heated above the transition point, with such ends being held by clamps which are shown in vertical section.

FIG. 6 is a side elevational view of another embodiment of the wire wherein the terminal end sections are each wrapped around a low mass heat insulator with the turns being close together to induce self-heating at the ends that are supported by the heat insulation and by clamps which are shown in vertical section.

FIG. 7 is a detailed cross-sectional view, taken substantially on line 77 of FIG. 6.

DESCRIPTION OF THE PREFERRED EMBODIMENTS Referring now more particularly to the accompanying drawing and, initially to FIG. 1, the hot wire relay type device 10 is composed of a wire body 12 formed from an alloy composition as specified or from any composition that exhibits the characteristic of mechanical shape memory as a result of martensitictype transformation. In its transition such wire body has a curve of increasing modulus with increasing temperature and another curve of decreasing modulus with decreasing temperature. This description applies to either Modulus of Elasticity or to Modulus in Torsion. In US. Pat. No. 3,403,238 to Buehler et al. FIG. 1 shows the flexing of a bar to demonstrate the Modulus of Elasticity while FIGS. 2 and 3 show a twisted member demonstrating the Modulus in Torsion. The wire body is stretched when it is cool and soft below its transition point and a current is then passed through the wire body to heat it above its transition point. The wire body which becomes much stronger overcomes the force tending to stretch it and returns toward its original unstretched length. The alternate stretching and contracting of the wire body can be utilized to operate a switch, valve, motor or other mechanical device.

In the embodiment of FIG. 1, the wire body 12 is work hardened and the main center section 14 of the wire is annealed so as to obtain a modulus change only in the uniformly heated center section 14. The end portions 16, which are anchored in the clamps 18, remain hard at all times and can be reliably clamped within the clamps 18. The center section 14 of the wire body 12 may be heated to annealing temperature by any convenient means such as applying current through the wire or passing such current through the wire or applying external heat thereto.

In FIG. 2, the hot wire relay-type device 20 is composed of a wire 22 formed of an alloy composition having the same unusual characteristic of shape or mechanical memory as the wire body 12 (FIG. 1 The wire body 22 has a main center section 24 terminating in end portions 26 which are treated so as to produce hardening by a process such as chromium infusion, with such thusly treated and resultingly hardened end portions 26 clamped within the holding clamps 28.

In FIG. 3, the hot wire relay type device 30 is composed of a wire body 32 having an elongated portion 33 formed entirely of an alloy composition having the characteristics of shape or mechanical memory as a result of martensitic-type transformation. The portion 33 is annealed and has its ends 34 welded, as at 35, to hard wire end portions 36 which end portions have no transition. The end portions 36 are anchored by means of conventional clamps 38. The portion 33 thus forms the active central portion of the overall wire including the welded-on end portions 36.

In FIG. 4, the hot wire relay type device 40 is composed of a single length of wire 42 formed from an alloy composition of any type that exhibits the unusual characteristics of mechanical or shape memory, as afore-defined, with the wire body having a helically coiled center portion 44. The helical coil configuration is constituted by outwardly diminishing diameter loops and at its ends with the outermost loops terminating in straight axial projections 46 that are held within clamps 48. The stress reduces as the mean diameter decreases with a low stress on the end portions 46 so that even though the ends heat slowly and remain below the transition temperature and thereby soft, the low stress required for proper operation of the device will not yield or become unstable in the clamp area.

In FIG. 5, the hot wire relay type device 50 is composed of a wire body 52 formed of an alloy composition exhibiting the unusual characteristic of shape or mechanical memory of the nature as defined in connection with the preceeding embodiments. The wire body 52 has a coating 53 that tapers from the center toward the opposing ends for the purpose of delaying heating of the center section 54 of the wire, the entire wire being annealed. The uncoated end portions 56 are anchored within the clamps 58. The coating 53 has a greater thickness at the middle or center of the wire than at the ends and the end portions 56 are free from any coating so that in this way the entire length of the wire will have an excellent thermally distributive heat characteristic.

In FIGS. 6 and 7, the hot wire relay type device 60 is composed of a wire body 62 formed from an alloy exhibiting the unusual characteristic of mechanical or shape memory as a result of martensitic-type transformation, as afore delineated. Each terminal section 63 (163) is wrapped in a number of side-by-side turns 64 (164) around a relatively large diameter, star-shaped or pointed low mass heat insulator 65 with the turns 64 (164) being close together, as shown in FIG. 7, so as to induce self-heating in each terminal section 63 (163), that is wrapped around its star-shaped insulator 65 (165). The self-heating of the terminal sections will cause them to heat at approximately the same rate as the rest of the wire body 62 so that thermal balance is achieved throughout the entire length of the wire. Each end portion 66 (166) of wire 62 is held by a clamp 68 (168). The star-shaped insulators 65 and 165 acts as a capstan, and the clamps 68 and 168, which are mounted on the same supporting base 69, prevent the terminal sections 63 and 163 from slipping on the starshaped insulators 65 and 165.

Inasmuch as the present invention is subject to many variations, modifications and changes in detail, it is intended that all matter contained in the foregoing description or shown in the accompanying drawing shall be interpreted as illustrative and not in a limiting sense.

What Is Claimed Is:

1. A heat reactive controller for actuators of the type used in hot wire relays and the like, said controller comprising an elongated wire having a center portion terminating in a pair of spaced opposite end portions, said wire being formed from a material having temperature actuated mechanical shape memory and having an initial shape above a predetermined transition temperature and a distorted shape below said predetermined transition temperature; and

a pair of spaced clamping means anchoring said end portions with said wire distorted under mechanical load below said predetermined transition temperature;

said center portion having a first hardness less than that of said end portions below said transition temperature and a second hardness substantially equal to that of said end portions at said transition temperature whereby heating of said wire to at least said transition temperature causes said wire to tend to resume its initial shape with substantially uniform hardness throughout the length of said wire.

2. The controller according to claim 1 wherein said center portion only is annealed to obtain a modulus of elasticity change in only said center portion with a change in temperature, the end portions anchored by the clamping means remaining hard at all times.

3. The controller according to claim 1 wherein said center portion only is annealed to obtain a modulus in torsion change in only said center portion with a change in temperature, the end portions anchored by the clamping means remaining hard at all times.

4. The controller according to claim 1 wherein said end portions are prehardened independent of temperature to have a hardness greater than that of said center portion below said transition temperature whereby the hardness of said end portion is substantially unaffected by said transition temperature.

5. The controller according to claim 1 wherein said end portions comprise hard wire segments having substantially no change in hardness at said transition temperature, said segments being welded to the wire fonning the center portion.

6. A heat reactive controller for actuators of the type used in hot wire relays and the like, said controller comprising;

an elongated wire having a center portion terminating in a pair of spaced opposite end portions, said wire being formed from a material having temperature actuated mechanical shape memory and having an initial shape above a predetermined transition temperature and a distorted shape below said predetermined transition temperature; and

a pair of spaced clamping means anchoring said end portions with said wire distorted under mechanical load below said predetermined transition temperature,

said center portion being helically coiled with outwardly diminishing diameter coils with the outermost loops terminating in straight axial projections forming said end portions, whereby stress on the end portions is reduced.

7. A heat reactive controller for actuators of the type used in hot wire relays and the like, said controller comprising:

an elongated wire having a center portion terminating in a pair of spaced opposite end portions, said wire being formed from a material having temperature actuated mechanical shape memory and having an initial shape above a predetermined transition temperature and a distorted shape below said predetermined transition temperature; and

a pair of spaced clamping means anchoring said end portions with said wire distorted under mechanical load below said predetermined transition temperature;

means to allow the end portions to heat at the same rate as the center of the wire, whereby heating of said wire to at least said transition temperature causes said wire to substantially unifonnly heat and tend to resume its initial shape with substantiaily uniform hardness.

8. The controller according to claim 7 further comprising a coating on said center portion, said coating having a greater thickness at the middle of said wire and tapering in thickness toward the ends, whereby heating of said center portion is retarded and said wire is substantially uniformly heated to achieve uniform hardness.

9. The controller according to claim 7 further comprising a pair of large diameter, low mass heat insulators spaced from each other on opposite ends of the center portions, each insulator being wrapped with turns of said wire, said turns being close together so as to induce self-heating of the end portions and thereby provide uniform heating in and uniform hardness of said controller.

10. The controller according to claim 9 wherein each said insulator comprises a star-shaped mass acting as a capstan. 

1. A heat reactive controller for actuators of the type used in hot wire relays and the like, said controller comprising an elongated wire having a center portion terminating in a pair of spaced opposite end portions, said wire being formed from a material having temperature actuated mechanical shape memory and having an initial shape above a predetermined transition temperature and a distorted shape below said predetermined transition temperature; and a pair of spaced clamping means anchoring said end portions with said wire distorted under mechanical load below said predetermined transition temperature; said center portion having a first hardness less than that of said end portions below said transition temperature and a second hardness substantiaLly equal to that of said end portions at said transition temperature whereby heating of said wire to at least said transition temperature causes said wire to tend to resume its initial shape with substantially uniform hardness throughout the length of said wire.
 2. The controller according to claim 1 wherein said center portion only is annealed to obtain a modulus of elasticity change in only said center portion with a change in temperature, the end portions anchored by the clamping means remaining hard at all times.
 3. The controller according to claim 1 wherein said center portion only is annealed to obtain a modulus in torsion change in only said center portion with a change in temperature, the end portions anchored by the clamping means remaining hard at all times.
 4. The controller according to claim 1 wherein said end portions are prehardened independent of temperature to have a hardness greater than that of said center portion below said transition temperature whereby the hardness of said end portion is substantially unaffected by said transition temperature.
 5. The controller according to claim 1 wherein said end portions comprise hard wire segments having substantially no change in hardness at said transition temperature, said segments being welded to the wire forming the center portion.
 6. A heat reactive controller for actuators of the type used in hot wire relays and the like, said controller comprising; an elongated wire having a center portion terminating in a pair of spaced opposite end portions, said wire being formed from a material having temperature actuated mechanical shape memory and having an initial shape above a predetermined transition temperature and a distorted shape below said predetermined transition temperature; and a pair of spaced clamping means anchoring said end portions with said wire distorted under mechanical load below said predetermined transition temperature, said center portion being helically coiled with outwardly diminishing diameter coils with the outermost loops terminating in straight axial projections forming said end portions, whereby stress on the end portions is reduced.
 7. A heat reactive controller for actuators of the type used in hot wire relays and the like, said controller comprising: an elongated wire having a center portion terminating in a pair of spaced opposite end portions, said wire being formed from a material having temperature actuated mechanical shape memory and having an initial shape above a predetermined transition temperature and a distorted shape below said predetermined transition temperature; and a pair of spaced clamping means anchoring said end portions with said wire distorted under mechanical load below said predetermined transition temperature; means to allow the end portions to heat at the same rate as the center of the wire, whereby heating of said wire to at least said transition temperature causes said wire to substantially uniformly heat and tend to resume its initial shape with substantially uniform hardness.
 8. The controller according to claim 7 further comprising a coating on said center portion, said coating having a greater thickness at the middle of said wire and tapering in thickness toward the ends, whereby heating of said center portion is retarded and said wire is substantially uniformly heated to achieve uniform hardness.
 9. The controller according to claim 7 further comprising a pair of large diameter, low mass heat insulators spaced from each other on opposite ends of the center portions, each insulator being wrapped with turns of said wire, said turns being close together so as to induce self-heating of the end portions and thereby provide uniform heating in and uniform hardness of said controller.
 10. The controller according to claim 9 wherein each said insulator comprises a star-shaped mass acting as a capstan. 